In the microelectronics industry, the trend is to reduce the size of structural features. Microlithography employing effective photoresists provides the enabling techniques. However, as the feature miniaturization continues, there is a need to decrease the photoresist thickness as well. For some lithographic imaging processes, the thin photoresist used in advance microlithography can no longer provide enough masking budget for the substrate etching in order to achieve pattern transfer with high fidelity.
One solution to this problem is the utilization of a layer underlying the photoresist, which not only functions as anti-reflective coating, but also provides sufficient etch selectivity. This enhanced etch selectivity will allow this underlayer to be used as an image transfer intermediate. In the current state-of-the-art technology development, silicon-containing bottom anti-reflective coatings are employed to serve this purpose.
For some lithographic imaging processes, the resist used does not provide sufficient resistance (masking) to subsequent etching steps to enable effective transfer of the desired pattern to a layer underlying the resist. In many instances (e.g., where an ultrathin resist layer is desired, where the underlying material to be etched is thick, where a substantial etching depth is required, and/or where it is desired to use certain etchants for a given underlying material), a so-called hardmask layer is used intermediate between the resist layer and the underlying material to be patterned by transfer from the patterned resist. The hardmask layer receives the pattern from the patterned resist layer and should be able to withstand the etching processes needed to transfer the pattern to the underlying material.
In cases where the photoresist does not provide sufficient dry etch resistance, a combination of underlayers with antireflective properties can act as a hard mask. Resist images can easily be transferred to a silicone containing antireflective coating by etching with a fluorinated gas since F is highly reactive to silicone functionalities which decomposes the coating into gaseous Si—F species. This is highly necessary when breaking through the Si hard mask. On the other hand, high Si content masks have superior etch resistance when oxygen gas is used during etching since SiO2 formation creates a hard mask while the organic underlayer is etched. Like photoresists, organic underlayers act as a mask for the substrate etch. In essence, a trilayer system is used with the goal of having both high etch resistance and low etch resistance under different conditions. In a trilayer system, a bottom layer (typically a carbon-based underlayer) is formed on a substrate (for example, Si-type), a silicon-based layer (Si-BARC) is coated over the bottom layer, and then a photoresist is formed over top of the silicon-based layer. Combining the requirements of elemental disparity between layers with antireflective properties is highly desirable for both lithography and pattern transfer.
Also, where the underlying material layer is excessively reflective of the imaging radiation used to pattern the resist layer, a thin antireflective coating is typically applied between the underlying layer and the resist layer. In some instances, the antireflection and hardmask functions may be served by the same material.
While many hardmask and antireflective coating materials exist in the prior art, there is a continued desire for improved compositions. Many of the prior art materials have stability issues, which decrease their shelf life, and thus are difficult to use. It would be desirable to have silicon-based antireflective coating/hardmask compositions that have increased stability and prolonged shelf life.